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58 PCB007 MAGAZINE I JUNE 2022 Chemical etching is a vital process for man- ufacturing PCBs. It is one of the most com- plex chemical processes next to plating. is is because there are many different variables that can affect your product and how efficiently it is produced. Although it is complex, etching of copper can be narrowed down to a handful of etchants that PCB manufacturers widely use. By far, the most common etchants are cupric chlo- ride and alkaline cupric chloride, commonly referred to as "ammoniacal alkaline etchant." ere are other etchants for copper, such as fer- ric chloride, sodium persulfate, and alkaline ammonia sulfate, but they are not commonly used for PCB manufacturing and are oen only used in "special cases." I may touch on those other etchants a bit more in a future column, but this one will focus on cupric and alkaline. About Cupric and Alkaline Together, these etchants are used in the majority of PCB etch shops, with alkaline being the most popular. To provide a baseline of how they work, their etch reactions along with their corresponding regeneration reac- tions, can be found in Table 1. One of the main reasons these two etchants are the most used is because of their regen- eration capabilities. With regeneration, you increase the capacity of copper you can etch. It also helps keep the etch rate at a consistent value. To maintain mass production of PCBs, it is important to keep the etch rate steady but also high enough to maximize output. Since etch rate can greatly influence produc- tion rates, it is a major factor when comparing etchants. Etchants of the Industry: Cupric vs. Alkaline The Chemical Connection by Christopher Bonsell, CHEMCUT

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